Add dotnet default solution to VSCode settings

A new settings.json file was created in the .vscode directory to specify the default solution for dotnet. This change is intended to make it easier for developers to work within the VSCode environment by automatically loading the 'Atc.Cosmos.sln' solution on startup.

Author: christianhelle

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "dotnet.defaultSolution": "Atc.Cosmos.sln"
+}